Some computing devices are available in foldable form factors that allow a device to be used in multiple physical configurations. For example, in one implementation, a computing device may have a display on two halves, wherein the two halves are separated by a hinge. In one physical configuration, the computing device may be used in a closed position (0°), wherein the displays on the two halves are folded about the hinge to face each other. In another configuration, the computing device may be used in an open position (180°), wherein the computing device is opened flat (e.g., on a table top) with the displays facing in the same direction (e.g., away from the tabletop). In a third configuration, the computing device may be used in a reverse-closed position (360°), wherein the displays on the two halves are folded about the hinge to face away from each other. Other configurations may position the halves in different angular orientations with respect to each other, such as at a 90° angle resembling a laptop computer configuration although other angles are also possible. Other form factors may provide very different physical configurations, including without limitation configurations including more than two device portions, a display half and a non-display half, sliding interfaces between device portions, and non-hinge interfaces.
The multiple physical configurations present a challenge when designing magnetic access to electromagnetic coils inside a computing device, particularly in the presence of metal casing, metal framing, and other metal components. The multiple physical configurations present an opportunity to use Near Field Communications (NFC) and inductive charging from multiple sides of the computing device in various physical configurations. Such metal structures, however, can fatally diminish operations that rely on internal electromagnetic coils. In fact, some designs have layered a ferrite sheet (or other material with high permeability) between an electromagnetic coil and such a metal structure to mitigate the degradation of the magnetic field by the metal structure, which acts as a ground plane. However, such a high permeability material limits omnidirectional performance of the coil, which is unsatisfactory for multi-configuration devices.